Work in the proposed project will continue to deal with interactions between sodium and calcium transport by renal epithelium. In addition, a re-investigation of the electrical potential profile along the nephron will be performed. Also, the effect of changes in protein concentration, in perfusion fluid, on proximal tubular reabsorption in perfused isolated rat kidneys will be assessed in microperfusion experiments (simultaneous use of isolated perfused kidney and microperfusion of proximal tubules by means of a pump).